1. Field of the Invention
The present invention relates to an injection-molded resin face gear used to allow power transmission and rotation transmission between two perpendicular axes.
2. Description of the Related Art
In recent years, in technical fields related to power transmission devices using gears, resin gears are used being in place of metal gears to achieve quieter operation noise, reduced weight, and lower costs.
Based on such technical background of recent years, there is discussion regarding forming a face gear 100, such as that shown in FIG. 9 and FIG. 10, using resin. In the face gear 100 shown in the drawings, a roughly disk-shaped web 102 is formed on an outer circumferential side of an axis section 101. A teeth section 103 is formed on an outer circumferential edge of the web 102. The teeth section 103 of the face gear 100 is formed such that teeth 104 of the teeth section 103 project towards one side surface 105 side. A plurality of teeth 104 are formed evenly spaced in a circumferential direction (refer to Patent Literature 1).
Patent Literature 1: Japanese Patent Laid-open Publication No. 2002-223673 (refer, in particular, to paragraphs 0004 to 0005, and FIG. 3 and FIG. 5)
However, when the metal face gear 100 such as that shown in FIG. 9 and FIG. 10 are simply formed using resin, as a result of shrinkage (formation shrinkage) of resin material after injection-molding, the outer circumferential edge side of the web 102 collapses (curves and becomes deformed) such that a tooth crest 106 moves in a right-hand side direction in FIG. 10. The teeth 104 collapse (the tooth crest 106 is displaced to a position indicated by 106′). Gear accuracy may deteriorate, thereby making accurate and smooth rotation transmission difficult.